* Fix unused variable warnings
These are now exposed because libprotobuf is no longer polluting the
compiler command-line with -Wno-unused-parameter.
* Convert (void)var to __unused where possible
* Test that shows a leak.
* Add EventListener to match Android.
* Use AsyncEventListener in FSTQueryListenerTests
* Remove FSTAsyncQueryListener
* Use EventListener throughout
Add option to allow the user to control where DocumentReference.getDocument() and CollectionReference.getDocuments() fetches from. By default, it fetches from the server (if possible) and falls back to the local cache. It's now possible to alternatively fetch from the local cache only, or to fetch from the server only (though in the server only case, latency compensation is still enabled).